The present invention relates to a vertical type injection molding machine that reduces the load on a motor that drives a movable mold.
Conventional injection molding machines include horizontal types in which clamping is performed along the installation surface, or along the horizontal direction and vertical types in which clamping is performed along the vertical direction. Since the movable mold of a horizontal type injection molding machine is moved horizontally, the movable mold is hardly influenced by the gravity unlike the movable mold in a vertical type injection molding, which is moved vertically. Thus, in a horizontal type injection molding machine, load imposed on the motor driving the movable mold is small, and the motor thus operates in a stable manner. On the other hand, since the movable mold in a horizontal type injection molding machine is permitted to move horizontally, the footprint of the machine is relatively large.
Vertical type injection molding machines are advantageous over horizontal type injection molding machines because of the smaller footprints. However, since the movable mold of a vertical type injection molding machine is greatly influenced by the gravity, the load imposed on the motor that drives the movable mold is relatively great. Accordingly, in order to reduce the load acing on the motor, for example, Japanese Laid-Open Patent Publication No. 08-52756 discloses a vertical type injection molding machine 100 including a fixed mold 101 and a movable mold 105 as shown in FIG. 8.
The vertical type injection molding machine 100 of FIG. 8 has a base 108 placed on the installation surface. Four support pillars 109 extend from the base 108. A ceiling portion 110 is provided on the support pillars 109. A stationary platen 117, which is fixed to the support pillars 109, is provided between the base 108 and the ceiling portion 110. The fixed mold 101 is fixed to and supported on the stationary platen 117, which has an upper surface parallel to the upper surface of the base 108. The stationary platen 117 support tie bars 116 that extend along the thickness of the stationary platen 117, or along the vertical direction, such that the tie bars 116 can slide along the vertical direction. The upper ends and the lower ends of the tie bars 116 are fixed to and support an upper platen 114 and a lower platen 115, respectively. The movable mold 105 is fixed to and supported on the lower surface of the upper platen 114 so as to face the fixed mold 101. Therefore, the upper platen 114, the lower platen 115, the tie bars 116, and the movable mold 105 are integrally raised and lowered, so as to form a movable body 106, which moves in the vertical direction. On the other hand, the stationary platen 117 and the fixed mold 101 form a fixed body 102.
Two pulleys 111a, 111b are provided on the lower surface of the ceiling portion 110. The first pulley 111a is located at an edge of the ceiling portion 110 (left edge as seen in FIG. 8), and the second pulley 111b is located substantially at the center of the ceiling portion 110. A wire 112 is placed over the pulleys 111a, 111b. An end of the wire 112 located closer to the first pulley 111a is connected to a weight 113 the weight of which is the same as the weight of the movable body 106. An end of the wire 112 located closer to the second pulley 111b is connected to the upper platen 114 of the movable body 106.
A mover mechanism 118 is provided between the stationary platen 117 and the lower platen 115. The mover mechanism 118 is driven by a motor 120 located below the lower platen 115 so as to move the movable body 106 in the vertical direction. Accordingly, the movable mold 105 is either brought closer to or moved away from the fixed mold 101.
The movable body 106 is pulled upward by a force corresponding to the weight of the weight 113 through the wire 112. Since the weight of the weight 113 is the same as that of the movable body 106, the movable body 106 and the weight 113 are balanced through the wire 112. That is, the movable body 106 never free-falls due to its own weight. Therefore, the motor 120 does need to be operated in order to maintain the movable body 106 at a prescribed position. This reduces the load imposed on the motor 120, which drives the movable body 106.
At injection molding using the injection molding machine 100, the movable mold 105 is clamped onto the fixed mold 101, and molten resin is injected into the cavity between the molds 101, 105 under a high pressure. The fixed mold 101 and the movable mold 105 are designed to be large and heavy so as not be deformed by molten resin that is injected under a high pressure. Since the wire 112 and the pulleys 111a, 111b support the weight 113 that weighs the same as the movable body 106, in addition to the movable body 106 including the heavy movable mold 105, the wire 112 might be stretched, and the pulleys 111a, 111b might be deformed. Extension of the wire 112 and deformation of the pulleys 111a, 111b hinders smooth rising and descending of the movable mold 105. As a result, the load imposed on the motor 120 is increased, making the operation of the injection molding machine 100 unstable.